The present invention relates to diesel fuel engines and, in particular, to a method and system for injecting natural gas into a diesel fuel engine for combustion therein.
The invention has been developed primarily with respect to conventional diesel fuel engines and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of us and is also applicable to bio-diesel fuel engines, for example.
Diesel fuel engines are used widely in a large array of applications such as transport, heavy machinery or power generation and form a significant component of much equipment in agriculture, mining, construction, and freight and passenger transport. The recent significant rise in the price of diesel fuels has added to the importance of maintaining diesel fuel engine equipment so as to allow them to operate as efficiently as possible. Relatively small efficiency gains can lead to a dramatic decrease in fuel consumption and equipment wear, together with corresponding reductions in pollution and other emissions.
It is known that a combustible gas can be added to a diesel fuel engine air intake. The mixture of the combustible gas with the conventional air intake enhances combustion conditions within the cylinder so as to increase efficiency of the diesel fuel combustion process. In the prior art, a combustible gas source, for example a natural gas source, is connected to an air inlet of a diesel fuel engine and injected by means of a solenoid valve, at some predetermined rate. This is drawn into the engine air intake stream and mixed in a venturi. The suction of the venturi is provided by the manifold vacuum or pressure difference.
Unfortunately, simple factors in engine performance deterioration significantly reduce the efficiency of the combustible gas injection and hence engine combustion. For example, as the diesel engine is operated, its air filter will naturally reduce the flow rate it allows into the engine air intake streams. As a result, the level of the combustible gas injected is not decreased proportionally. As a further result, the prior art disadvantageously start to decrease in any delivered efficiency gains and, depending on the deterioration of engine components such as the air filter, can do more harm than good by providing conditions in which the engine efficiency is lower with a combustible gas injection than without.
It is the genesis of the present invention to provide a method and system of injecting methane, natural gas or substitute natural gas into a diesel fuel engine for combustion with diesel fuel therein which will overcome or substantially ameliorate one or more of the disadvantages of the prior art, or to provide a useful alternative.